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form a layer round the orifice of the inlet tube with the soda-
lime above.

The joints being tight, the mixture of 25 grams of alcohol and
i 50 grams of sulphuric acid is run into the large flask containing
a little dry sand and heated with a small flame on the sand-bath
until a steady stream of gas is evolved. When this occurs the
mixture of alcohol and sulphuric acid is dropped in slowly from
the tap-funnel. It is important to moderate the temperature
to prevent excessive frothing and the separation of carbon,
which, however, cannot altogether be avoided. A considerable
quantity of sulphur dioxide which is evolved with the ethylene

FIG. 50.
is removed by the caustic soda in the wash-bottles. If the
water surrounding the bromine bottles becomes warm, small
lumps of ice should be thrown in. The caustic soda should
be occasionally renewed, otherwise sulphur dioxide may pass
into the bromine and reduce it to hydrobromic acid. If the
pressure in the apparatus causes a back rush of bubbles
through the tap-funnel attached to the flask, the difficulty is
met by inserting the stopper in the tap-funnel. After a
few hours the bromine in both vessels is decolourised or at
least changes to a straw colour. The crude ethylene bromide
is removed and shaken with dilute caustic soda solution, then
with water, separated from the aqueous layer and dehydrated